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The purpose of this study was to examine the direct and indirect effects of ultraviolet-B (UV-B) radiation on freshwater protists. Laboratory experiments were conducted in order to determine the importance of photoenzymatic repair (PER) of UVBinduced DNA damage in the heterotrophic nanoflagellate Paraphysomonas sp. Investigations into the combined effects of UV-B and chromophoric dissolved organic matter (CDOM) were conducted in laboratory experiments in which protist cultures were exposed to UV-B radiation in the presence and absence of water amended to a higher CDOM concentration in order to determine the ability of CDOM to act as a UV-B filter and as a potential nutrient source. Field experiments examined the responses of natural communities of protists and bacteria to ultraviolet radiation (UVR) in the presence of high and low concentrations of CDOM. Ultraviolet-B radiation (UV-B; 280 – 320 nm) negatively affects many aquatic organisms, including heterotrophic flagellates, by directly damaging DNA. The quantity of UV-B reaching the surface of a lake varies with atmospheric chemistry, including stratospheric ozone, and the presence of large holes (Alldredge 1977) in this ozone shield during the last decade resulted in historically high UV-B levels. In aquatic systems, the nature of the damage to organisms depends on the intensity and duration of solar radiation, plus its attenuation in the water column. The amount of UV-B damage is highly dependent on the concentration of CDOM in the water column because CDOM strongly absorbs UV-B radiation. This protective role of CDOM is likely to be reduced in areas where warmer, drier climate decreases watershed runoff, which ultimately results in acidification and increased CDOM photodegradation. However, CDOM also may also act as an organic carbon source for bacteria and stimulate growth of the microbial food web, including bacterivores like heterotrophic flagellates. The effect of UV and CDOM interactions on the microbial food web is not well understood, but climate-related increase in CDOM in an oligotrophic lake could increase the heterotrophic microbial food web impact by reducing UV-B damage and increasing available resources. Since aquatic organisms, including protists, are differentially susceptible to UV-B radiation, climate change effects on CDOM and UV-B attenuation are likely to alter the ecology and community structure of aquatic systems. This thesis describes investigations into the direct and indirect effects of UV-B radiation on freshwater protozoa. The role of PER of direct UV-B induced DNA damage was examined in laboratory experiments that compared the survival and population growth of the heterotrophic nanoflagellate Paraphysomonas sp. at two environmentally relevant temperatures. The results from these experiments demonstrated the reliance of Paraphysomonas sp. on PER, with 100% mortality in the absence of the photorepair radiation that activates photoenzymatic repair enzymes. The ability of Paraphysomonas sp. to recover from exposure to UV-B radiation declined in flagellates adapted to 15°C relative to the same exposures at 20°C. Experiments examining the direct and indirect effects of UV-B radiation and CDOM on freshwater protists conducted in the laboratory and in an oligotrophic lake in the Pocono Mountains showed that potential DNA damage resulting from UV exposure is reduced and microbial growth may be enhanced with an increase in CDOM concentration. / Biology

Increasingly higher numbers of people are moving into urbanizing environments, yet our understanding of ecosystem consequences of rapid urbanization is still in its infancy. In this dissertation, I assessed dynamics of residential landscapes during suburban succession and consequences for ecosystem functioning. First, I used a space-for-time approach to quantify more than a century of suburban succession in the Dallas – Fort Worth metroplex (DFW). Attributes of residential landscape plant diversity and habitat complexity were quantified for 232 individual properties nested within 14 neighborhoods constructed between 1906 and 2020. Suburban succession progressed from simple turf lawns with limited habitat complexity to landscapes dominated by deciduous trees and high habitat complexity, but homeowner decisions related to landscape management affect the rate of that transition and the number of plants and taxa present. Next, I used the novel spatial construct of "neighborhoodsheds" to test for effects of suburban succession on carbon export, and found that the proportion of carbon derived from C3 vs. C4 plants was affected by neighborhood plant community structure (i.e. greater proportion of trees and shrubs primarily in later stages of suburban succession). Finally, I conducted a mesocosm experiment to test effects of changes in allochthonous inputs during suburban succession on aquatic ecosystem functioning. The proportion of carbon from C3 vs. C4 sources interacted with time to affect abundance of emergent mosquitoes and chironomids. This work sets the stage for further research on urban ecology in DFW and provides conceptual advances for the study of urban ecosystems more broadly.

American Kestrels (Falco sparverius) are a small falcon with an expansive range across North America. However, kestrels have been reported to be declining since the 1960s, with the primary cause of decline unknown. With previous research focusing on the summer breeding season, researchers have called for additional investigation in understudied wintering and migratory periods. In Chapter 2, I quantified annual survivorship against five covariates of migrant kestrels wintering in north Texas to contribute to population level analyses across the kestrel's expansive range. Notably, I found that juvenile survival is similar to that of adults once on the wintering grounds, and that aspects of urbanization may increase survival in wintering kestrels. In Chapter 3, I outlined kestrel movement ecology by quantifying migration phenology, performance, and patterns. Additionally, I identified breeding and stopover sites and analyzed both winter and summer home ranges. In this analysis, I contributed three additional migration tracks to the five currently published. Further, I reported the first loop and indirect migration patterns to our knowledge. Overall, this research highlights understudied aspects of the kestrel full annual cycle in the winter and migratory periods, providing insight into possible causes for kestrel declines.

I surveyed macroinvertebrate assemblages in ponds in three grazing regimes (ungrazed, rotationally grazed, and continuously grazed) in spring and summer of 2019 on the Osage Plains ecoregion of Missouri. Total suspended solids, turbidity, and organophosphates were lower in ungrazed ponds than in both grazed treatments, and water transparency and aquatic macrophyte cover was significantly higher. Richness was positively correlated with average depth, deepest depth, and water transparency and negatively correlated with turbidity and organophosphate levels. Overall, ungrazed ponds supported higher taxa richness and diversity across all taxa, as well as higher Diptera: Chironomidae, Odonata, and Trichoptera richness. Ungrazed ponds contained 29 unique genera and three unique families compared to two unique genera and two families in rotationally grazed ponds, and one 6 unique genera and one family in continuously grazed units. PerMANOVA results confirmed differences in habitat variables between ungrazed treatments and both grazed treatments; PCA analysis indicated that decreased taxa abundances were mostly associated with nitrate, bank slope, temperature, and pH and, while transparency and vegetation (emergent and cattails) were associated with increased abundances. PerMANOVA results confirmed seasonal differences in ungrazed ponds and continuously grazed treatments for total taxa and families. Chironomid communities differed between treatments and between seasons for ungrazed ponds and both grazing treatments. Fish presence reduced abundance of total taxa across seasons and in spring and Chironomidae taxa across seasons.

Urban acoustic ecology is an emerging field focused on furthering our understanding of how the sounds within urban development impact the surrounding soundscape and biodiversity. Human noise, otherwise known as anthrophonies, are known to negatively impact wildlife by impeding communication and lowering species richness. With urban population expected to grow profoundly within the next 30 years, it is critical to explore the acoustical relationship between the environment and wildlife for future management and urban development planning. I investigated how the physical landscape impacts the urban/peri-urban soundscape through acoustic indices within the greenspaces of Denton, Texas. Specifically, I found that the percentage of impervious surfaces have a significant negative impact on the coefficient of variation of the acoustic index ADI (Acoustic Diversity Index). ADI is used to calculate the occupancy of sounds within a frequency wave. Further, I investigated how the combination of landscape characteristics and acoustic indices predict avian species richness and rarity. My results show that richness and rarity was positively related to ADI; on the other hand, a soundscape with higher ADI (CV) scores, meaning consistent anthrophonies such as distance vehicle traffic, was related to higher richness and rarity. My research indicates that there is a relationship between the physical environment, ADI, and avian richness and rarity which showcases how acoustic monitoring can be a valuable tool for management and development protocols.

Tardigrades are microscopic organisms found in both terrestrial and aquatic environments, adapted to a wide range of environmental conditions. Despite their adaptability, tardigrade ecology, particularly their spatial distribution, remains an understudied topic. In this study, we provide a brief overview of tardigrades identified from 26 forests in Southern Chile. We represent tardigrades using Operational Taxonomic Units (OTUs) and examine their spatial distribution across multiple spatial scales. The finer scale involves individual samples (3 x 3 cm, ~9 cm2), while the larger scale encompasses the entire site from which samples were collected (10 x 10 km, 100 km2). We assessed both alpha and beta diversity at these finer and larger scales to determine the impact of these scales on their distribution. Additionally, we assessed whether geographical distances influence species turnover. Our results indicate that the composition and the assemblages of tardigrades varies greatly among samples and among sites. Different sites and scales significantly impact the spatial distribution of tardigrades. Moreover, we found nestedness was low but turnover was high across all the sites, and that geographical distance among sites does not impact turnover. Investigating how tardigrade diversity varies with scale, enhances our understanding of ecological dynamics.